The present invention generally relates to photochromic articles that include benzopyran compounds and benzopyran compositions. More specifically, the present invention relates to photochromic articles that include benzopyran compounds and benzopyran compositions.
Photochromism generally concerns the ability of a compound to reversibly change color under different light conditions. One particular type of photochromic phenomenon concerns the reversible change in color of a compound from an original color to a different color when the compound is exposed to a source of ultraviolet radiation, such as solar radiation or light radiated from a mercury or xenon lamp. The photochromic compound fades to the original color within a period of time after the compound is isolated from the ultraviolet radiation, such as by placing the compound in a dark room.
Various products, including optical lenses, incorporate the principal of photochromism. For example, photochromic compounds, such as naphthopyrans, are incorporated into plastic ophthalmic lenses to effect color changes in the plastic lenses when the lenses are exposed to particular lighting conditions. Additionally, different photochromic compounds may be blended to create a color effect that is different from the respective color effects of the individual photochromic compounds. As an example, a first photochromic compound that turns orange or red when activated by light and a second photochromic compound that turns blue when activated by light may be blended to form a photochromic mixture that produces a shade of gray when activated by light.
Several types of photochromic compounds have been reported which exhibit changes in color when exposed to ultraviolet light. One particular class of photochromic compounds includes the 3,3-disubstituted naphthopyrans. One specific group of 3,3-disubstituted naphthopyrans includes the 3H-naphtho[2,1b]pyrans. The color response of the 3H-naphtho[2,1b]pyrans to ultraviolet light extends to purple, red, orange or yellow, depending upon the composition and structure of the particular 3H-naphtho[2,1b]pyran. A general expression of the 3H-naphtho[2,1b]pyrans is provided in graphical formula I: ##STR2## where R.sub.1 and R.sub.2 are substituents attached to the pyran ring at the position indicated.
Several photochromic compounds are described in U.S. Pat. No. 3,567,605 to Becker. The Becker patent describes chromenes and chromene derivatives which are photochromic at relatively low temperatures. The patent also describes chromenes and chromene derivatives which are photochromic at room temperature, such as diphenyl-3H-naphtho[2,1b]pyran, where R.sub.1 and R.sub.2 of formula I are each unsubstituted phenyl groups.
Additional photochromic compounds are described in U.S. Pat. No. 4,931,221 to Heller et al. One type of photochromic compound described in Heller generally has the form of graphical formula I with R.sub.1 and R.sub.2 being cyclopropyl radicals and with any of various substituents included on the naphtho portion of the naphthopyran rings. Heller reports a larger bathochromic shift in the visible spectrum of 3H-naphtho[2,1b]pyrans that include the cyclopropyl radicals, as compared to 3H-naphtho[2,1b]pyrans that include alkyl groups or a spirocycloalkyl group in place of the cyclopropyl radicals.
Other photochromic compounds are described in U.S. Pat. No. 5,066,818 to Gemert et al. One photochromic compound class described in Gemert generally meets graphical formula I with one of R.sub.1 and R.sub.2 being a substituted phenyl radical, with one of R.sub.1 and R.sub.2 being either a substituted or unsubstituted phenyl radical, and with various substituents included on the naphtho portion of the naphthopyran rings. Gemert lists various non-aryl groups as potential substituents of the phenyl radicals of R.sub.1 and R.sub.2. Gemert reports a range of decolorization rates associated with the 3H-naphtho[2,1b]pyrans that include the phenyl radicals as R.sub.1 and R.sub.2.
Additional photochromic compounds are described in U.S. Pat. No. 5,106,998 to Tanaka et al. Tanaka describes compounds in which R.sub.1 and R.sub.2 of graphical formula I are alkyl groups. Tanaka reports several fade times and maximum absorption wavelengths associated with various 3H-naphtho [2,1b]pyrans that include the alkyl radicals as R.sub.1 and R.sub.2 in formula I.
U.S. Pat. No. 5,238,981 to Knowles teaches a 3H-naphtho [2,1b]pyran compound in which R.sub.1 and R.sub.2 of graphical formula I are each selected from a group of organic radicals that includes phenyl and naphthyl. The organic radicals placed at R.sub.1 and R.sub.2 are either substituted or unsubstituted. Potential substituents of substituted organic radicals placed at R.sub.1 and R.sub.2, provided that one of the organic radicals placed at R.sub.1 and R.sub.2 is a phenyl group, include various non-aryl groups. Various potential substitutions on the naphtho portion of the naphthopyran ring are taught, including an 8-methoxy substitution. Knowles states that the number eight carbon atom substitutions, such as the 8-methoxy substitution, cause a bathochromic shift in the visible spectrum associated with activated forms of the 3H-naphtho[2,1b]pyrans and in the ultraviolet spectrum of unactivated forms of the 3H-naphtho[2,1b]pyrans.
Additional photochromic compounds are described in U.S. Pat. No. 5,244,602 to Van Gemert. Van Gemert describes 3H-naphtho[2,1b]pyrans in which R.sub.1 and R.sub.2 of graphical formula I are each phenyl, naphthyl, various heterocyclic groups, and certain non-aryl groups. Van Gemert also discusses substitution of various non-aryl substituents into any phenyl, naphthyl, heterocyclic, and non-aryl groups placed at R.sub.1 and R.sub.2. Van Gemert also states that certain substitutions at the number 5 carbon on the naphtho ring causes a bathochromic shift of the absorption maximum of the 3H-naphtho[2,1b]pyrans.
U.S. Pat. No. 5,274,132 to Van Gemert describes certain 3H-naphtho[2,1b]pyrans in which R.sub.1 of graphical formula I is a phenyl group, a naphthyl group, a furyl group, or a thienyl group and in which R.sub.2 of graphical formula I is an arylalkenyl radical. Van Gemert describes a bathochromic shift associated with the 3H-naphtho[2,1b]pyrans that include the arylalkenyl radical, relative to certain other naphthopyrans disclosed in U.S. Pat. No. 3,567,605.